The present invention relates to a rotary compressor which may be advantageously employed in an air conditioning system of an automotive vehicle for compressing a refrigerant fluid.
Rotary compressors are well known in the art which comprise a housing formed with a bore, fluid inlets and outlets communicating with the bore and a rotor mounted in the bore in such a manner that rotation thereof causes a working fluid such as a refrigerant to be compressively displaced from the inlet to the outlet. The rotor is typically provided with radial slots and vanes which are slidably retained in the slots and urged into sealing engagement with the inner wall of the bore. The rotor is eccentrically or similarly disposed in the bore in such a manner that upon rotation of the rotor the vanes divide the bore into fluid chambers of progressively varying volume. The compressor is designed so that the fluid chambers increase in volume in the vicinity of the inlet and decrease in volume in the vicinity of the outlet so that the fluid is sucked into the fluid chambers through the inlet and discharged therefrom through the outlet at elevated pressure. Due to the sealing effect of the vanes the compressor operates on the positive displacement principle.
A unique method has recently been devised to lubricate the rotor without the provision of a separate oil pump. An oil sump is provided below the compressor housing which communicates with the fluid outlet. In this manner, the oil in the oil sump is subjected to the output pressure of the fluid. An oil passageway leads from the oil sump through the inner portion of the rotor to the fluid inlet in such a manner that oil is forced from the pressurized oil sump through the interior or the rotor to the low pressure fluid inlet.
The rotor comprises a drive shaft and a rotor body fixed to the shaft, the vane slots being formed in the rotor body. The oil passageway leads through the radially inner portions of the vane slots between the vanes and the shaft so that the pressurized oil not only lubricates the areas of sliding contact between the vanes and the walls of the respective slots but also urges the vanes radially outwardly into sealing engagement with the inner wall of the bore.
The oil is sucked along with the working fluid into the fluid chambers in the bore and lubricates the areas of sliding contact between the outer ends of the vanes and the wall of the bore. At the fluid outlet, the oil is separated from the working fluid and returned to the oil sump.
Although this basic design provides extremely efficient compressor operation and enables a substantial reduction in the number of component parts, a problem is encountered when the compressor is stopped. Even after the rotor movement is stopped, a substantial pressure difference exists between the fluid inlet and outlet which causes oil to flow through the oil passageway. Although the inlet and outlet pressures eventually reach equilibrium, the oil which flows after the compressor is stopped is of considerable volume and often fills the fluid inlet. As a result, when the compressor is again started, a hydraulic shock or "oil hammer" is produced which is capable of damaging the compressor.